The efficiency of 1,5-bis(4-dithiocarboxylate-1-dodecyl-5-hydroxy-3-methyl-pyrazolyl)penta ne (BDTCPP) as copper corrosion inhibitor in 3.5% NaCl solutions was studied by electrochemical polarization methods (Tafel extrapolation and polarization resistance method), electrochemical impedance spectroscopy and immersion assays. Results obtained in this study reveal that BDTCPP is a good inhibitor and the potentiodynamic polarization studies clearly show that BDTCPP is a mixed-type inhibitor for copper in chloride solutions. It decreases the anodic reaction rate more strongly than the cathodic reaction rate and it renders the open circuit potential of copper more positive in 3.5% NaCl solutions. The UV analysis of the protective layer of BDTCPP after corrosion experiments shows that the inhibitor prevents copper corrosion by physisorption on the metal surface, followed by chemisorption of a protective Cu(II)-complex. This Cu(II) is generated by oxidation of the Cu(I) ion formed at the beginning of the corrosion process in the aerated solution of NaCl.